Ruggedized rocking shaft

ABSTRACT

A calibration arm assembly for a servo-pneumatic altimeter is connected to avoid degrading torque conditions so that the original sensing of the pressure actuated mode is maintained. The assembly includes a generally L-shaped support having a base, a vertical arm and crank arm extending transversely between the top portion of the vertical arm and the rocking shaft for locating the support alongside the rocking shaft. The base of the support mounts one end of a bimetallic temperature compensator in nominally parallel relationship with the rocking shaft, the other end of the compensator being pin-connected with a link connected with the altimeter pressure capsule. The support is configured so that the axis of the link is substantially coplanar with the axis of the crank arm to accommodate opposing forces without developing torque about the axis of the crank arm.

United States Patent 2,166,603 7/1939 Menzer 73/386 FOREIGN PATENTS 903,l 86 8/1962 Great Britain Primary Examiner-Donald O. Woodiel ABSTRACT: Acalibration arm assembly for a servo-pneumatic altimeter is connected toavoid degrading torque conditions so that the original sensing of thepressure actuated mode is maintained. The assembly includes a generallyL- shaped support having a base, a vertical arm and crank ann extendingtransversely between the top portion of the vertical arm and the rockingshaft for locating the support alongside the rocking shaft. The base ofthe support mounts one end ofa bimetallic temperature compensator innominally parallel relationship with the rocking shaft, the other end ofthe compensator being pin-connected with a link connected with thealtimeter pressure capsule. The support is configured so that the axisof the link is substantially coplanar with the axis of the crank arm toaccommodate opposing forces without developing torque about the axis ofthe crank arm.

PAT-ENTEU JUN29 I9?! SHEET 1 BF 2 "PRIOR ART INVENTOR James ATTYPATENTEB JUN29 I911 3.589.195

SHEET 2 UF 2 INVENTOR James W. Angus ATTY.

RUGGEDIZED ROCKING SHAFT BACKGROUND OF THE INVENTION CROSS-REFERENCESThe following U.S. Pats. are assigned to the assignee of the presentinvention:

Andresen, U.S. Pat. No. 3,l60,0l2

Angst, U.S. Pat No. 2,689,480

The present invention relates generally to servo-pneumatic aircraftinstruments and, more particularly, to an improved calibration armassembly for determining the motion transfer between an altimeterpressure capsule and rocking shaft.

Servo-pneumatic altimeters, such as disclosed in Andresen U.S. Pat. No.3,160,012, incorporate a control system wherein a pressure actuatedaltimeter mechanism is overriden so that the altimeter indicatingpointer is positioned in accordance with an entirely separate, remotesource of information, Briefly, in the above patent an instrumentpointer shaft is directly driven according to a parameter which iselectrically transmitted to the instrument and, responsive to a failurethereof, the instrument reverts to a direct pressure actuated mode ofoperation. A signal representative of the difference between thetransmitted electrical parameter and the position of the pointer (asdetermined by a pressure sensitive diaphragm) is amplified and appliedto drive the rotor of a drag-cup motor, which is mechanically connectedwith the pointer shaft, until the shaft position agrees with thetransmitted electrical parameter. Accordingly, the pointer shaft of theinstrument is accurately positioned by the electrical systemindependently of the instrument pressure sensing components. In doing soit must overcome by force the pressure sensing mechanism in theindicatorv In the above patent, the calibration arm assembly is shown tocomprise the crank-link assembly connecting the pressure capsule androcking shaft. Thus, by changing the effective leverage length of thecrank, the motion transfer function rela tion between the rocking shaftand pressure capsule can be varied. The calibration arm assembly of theabove patent dif fers from the assembly of the present invention in thatno facilities are provided whereby the determined function relation canbe corrected for temperature fluctuation.

A calibration arm assembly that does provide for such a temperaturecorrection is as shown in FIG. 5 of U.S. Pat. No. 2,689,480 referencedabove. Briefly, the temperature compensator of that patent is shown tocomprise a bimetallic member or strip which is supported in nominallyparallel relationship with respect to the rocking shaft. The arrangementis such that the distance of the bimetallic member from the rockingshaft is variable without disturbance of the parallel relationship. Suchis accomplished by securing the bottom end of the bimetallic member to acrank arm which extends transversely between the bimetallic member androcking shaft. The top end of the bimetallic member is provided with ahead and a link is pin-connected between the head and the pressurecapsule. The arrangement permits manual and automatic adjustment of theeffective leverage length of crank arm at which the link acts on therocking shaft. That is, the link can be manually adjusted by loosening asetscrew which bears against a flat portion of the crank arm internallyof the rocking shaft and manually increasing or decreasing the distancebetween rocking ROCKING shaft and bimetallic member. Changes intemperature automatically cause the bimetallic member to flex therebyaltering the effective length of the crank arm at which the link acts onthe rocking shaft.

Because of the criticality of temperature correction of the motiontransfer function relation, the calibration arm assembly of U.S. Pat.No. 2,689,480 has been incorporated into altimeters of the type shown inU.S. Pat. No. 3,160,012. While the result has been an altimeter ofexcellent sensitivity and of proven reliability, it has been noted thatsuch instruments are subject to somewhat degraded performance when theyrevert to the pressure actuated mode after a period of use withexcessive correction being applied.

SUMMARY OF THE INVENTION The present invention has shown that a torqueabout the axis of the crank arm results from the offset between the lineof action of the diaphragm and the line of action of the crank arm. Inthe servo-pneumatic altimeter this torque is dependent upon the level ofthe opposing forces existing while motion is transmitted due to theaction of the electrically powered servomechanism overriding thepressure actuated mechanism of the total system.

It has been shown that the torque acting about the axis of the crank armproduces wear in the form ofimpressions made on the crank arm by thesetscrew which anchors the arm to the rocking shaft. These indentationscan occur after a period of normal use or can occur more rapidly whereunusual force levels are encountered. The indentations allow the crankarm to rotate a small angle (on the order o1f0.6) thereby affecting theaccuracy of the motion transfer function between the pressure capsuleand the rocking shaft when the altimeter reverts to its pressureactuated mode.

In accordance with the present invention, a calibration arm assemblyincorporates a support for the compensating means so that the axis ofthe link that connects to the compensating means is substantiallycoplanar with the axis of the crank arm to enable transmission ofopposing forces between the capsule and rocking shaft free of torqueabout the axis of the crank arm.

Other features and advantages of the invention will be apparent from thefollowing description and claims and are illustrated in the accompanyingdrawings: which show structure embodying preferred features of thepresent invention and the principles thereof, and what is now consideredto be the best mode in which to apply these principles.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings forming apart of the specifi cation, and in which like numerals are employed todesignate like parts throughout the same:

FIG. 1 depicts in simplified manner the elements comprising an altimeterincorporating a calibration arm assembly of the present invention;

FIG. 2 depicts a prior art calibration arm as incorporated into analtimeter of FIG. 1;

FIG. 3 is a top plan view ofa calibration arm assembly of the presentinvention and shows the assembly connecting the link with the rockingshaft;

FIG. 4 is a side elevational view of the calibration arm assembly ofFIG. 3; and

FIG. 5 is a perspective view of the calibration arm assembly with thebimetallic temperature compensator removed.

DETAILED DESCRIPTION Turning now to the drawings and specifically toFIG. 1 there is shown a servo-pneumatic aircraft altimeter incorporatingthe calibration arm assembly 1 of the present invention.

Briefly, the altimeter depicted in FIG. I incorporates an aneroid systemcomprising a diaphragm type pressure capsule 2 which expands andcontracts in response to static pressures applied thereto. The output ofthe diaphragm or capsule 2 is a linear function which is transmitted toa rocking shaft 3 which operates in a rotary function. The rocking shaft3 drives gear sector 10 which is typically designed such that a fulldeflection of diaphragm 2 will result in approximately full rotation ofpinion ll. Rotation of the pinion 11 is transmitted to rotary motion ofthe instrument output shaft 14 through the gear train comprising gears12, 13, 15 and 19. In the altimeter of FIG. 1, the gear train isdesigned such that the output shaft 14 will be caused to rotate one fullrevolution for each 1,000 feet of altitude.

Certain characteristic errors are inherent to the pneumatic drivemechanisms which can be predicted. One manner for correcting for sucherrors is to utilize a servo-drive system to override the pneumaticdrive system. Accordingly, synchro control transformer 18 receivessignals from a remote on board computer (not shown) and directs thedrag-cup motor 16 to apply a torque to position the indicator 17 indefiance to the pressure actuated system. Thus, if the position ofpointer 17 as represented by the output of synchro 18 is different fromthe position represented by the remote signal of the onboard computer,an error signal is delivered to an amplifier (not shown) which energizesthe drag-cup motor 16 so that the torque thereof depends upon themagnitude of the error signal while the direction of rotation of motor16 depends upon the sense of the error signal. When the error signalapproaches zero the altimeter indication will approach that determinedby the computer. In the event of a power failure or electrical malfunction, or when the servo becomes inoperative, the servo 18 isdeenergized and the pointer 17 immediately returns to the positiondetermined by the pressure capsule 2.

The present invention relates to the calibration arm as sembly which, asshown in FIG. 1, connects the rocking shaft 3 (rotating function) andthe diaphragm 2 (linear function) which is used to calibrate the motiontransfer function therebetween. To facilitate understanding of theinvention, reference ismade to a prior art calibration arm assembly, asshown in FIG. 2, that corrects for temperature fluctuation. This priorarrangement includes a support 6' and a crank arm 7 extendingtransversely between the rocking shaft 3 and the support 6 to carry thesupport alongside the rocking shaft. A temperature compensator whichcomprises a bimetallic member or strip, is shown having one end mountedon a cylindrical arm 58' and having its other end carrying a head 5A. Alink 4 is pin-connected to the head 5A. The crank arm 7 projects into atransverse bore in the rocking shaft and is adjustably mounted thereinby means of a setscrew 8' which bears against a flat portion provided onthe crank arm 7.

Inaccurate indications have been discovered in some of the priorcalibration arm assemblies when the altimeter reverts to its pressureactuated mode but the underlying problem has proven difficult toidentify. Recognition of the fundamental problem is an important aspectof the present invention.

In this respect, it will be noted that in the arrangement shown in FIG.2 an offset exists between the crank arm 7' and link 4'. When the servomakes a correction due to a difference between the pneumatically sensedaltitude and the computed altitude, the mechanical elements arepositioned against the action of the diaphragm 2 which acts as a spring.The diaphragm 2 exerts a resistive force against the calibration armassembly which results in a torsional reactance at the point where thecrank arm 7' is attached to the rocking shaft 3. Typically, the diameterof the crank arm 7 at the point of attachment is between one-sixth andthree thirty-seconds inch. It has been discovered that if a torque istransmitted through this attachment, the crank arm tends to rotate andan impression is made into the arm by the setscrew 8 allowing the crankarm 7' to rotate a small angle (approximately 0.6) which results in adegraded indication when the altimeter reverts to its pressure actuatedmode. The space limitations and degree of access and adjustment precludeutilization of heavier parts such as would minimize this problemv In apreferred embodiment in accordance with the present invention, thecalibration arm assembly places the attachment point of the crank arm 7in line with the resistive force of the diaphragm 2 thereby eliminatingthe torsion condition at the anchoring setscrew 8. In the preferredembodiment shown in FIG. I, the calibration arm assembly includes anL-shaped support 6 that accomplishes this function without losing any ofthe accessibility or adjustability required of the part. Tests haveshown this design to be impervious to the offset problem previouslyexperienced.

As best shown in FIG. 5, the generally L-shaped support 6 is a one-piecemetal casting having a base 21, an upstanding arm 20 carried on the baseat one edge thereof, and an integral crank arm 7 projecting sidewaysfrom the top of the arm 20.

The base 21 has a clamping socket 22 bordered by jaw portions 24 thatare controlled by a screw 23.

The upstanding arm 20 has a concave groove 25 along its inside face toprovide clearance for off axis deflection of the temperaturecompensator. The crank terminates in a threaded portion 78 projectingthrough the transverse bore in the rocking shaft to receive an anchornut 30 that fixes the lengthwise position of the crank arm so that anintermediate flat portion 7A is in registry with the setscrew 8.

The temperature compensator 5 is a bimetal element of rectangular shape.As best shown in FIG. 4, the compensator 5 is equipped with a mountingplug 58 that is received in the clamping socket 22 and an adapter head5A that provides a pin joint connection for link 4.

The support 6 is mounted adjacent a flat lengthwise portion 3A ofrocking shaft 3 with the vertical support arm 20 parallel to the axis ofrocking shaft 3 and with the crank arm 7 extending through the rockingshaft 3. In order to accurately calibrate motion between the pressurecapsule 2 and rocking shaft 3, a spring 28 is secured to the flat 3A ofrocking shaft 3 by pin 31 so that the support 6 is biased away from therocking shaft. The proper distance between the axis of the rocking shaftand the pivot axis (provided by head 5A for link 4) which determines theeffective leverage length of link 4 relative to the rocking shaft isestablished by adjustment of nut 30. When the proper distance has beenestablished, the setscrew 8 is tightened against the flat 7A of crankarm 7.

As is the case with the prior art arrangement, the arrangement of thepresent invention is such that the distance of the head 5A from therocking shaft 3 is variable without disturbance of the parallelrelationship of the bimetallic compensator 5 with respect to the rockingshaft 3. For this purpose, the one piece support 6 includes a dependingguide portion 26 provided with a U"-shaped slot 27 for axial movementalong pin 31.

Changes in temperature cause the bimetallic compensator 5 to flex. Inthe position shown the bimetallic compensator 5 tends to increase anddecrease, in dependence upon temperature, the effective leverage lengthof the crank arm 7 at which link 4 acts on the rocking shaft. Theinfluence of the bimetallic compensator 5 may be lessened by turning itssupporting cylindrical arm 5B relatively to the horizontal support arm21 after loosening of the screw 23.

It will be noted that in the present arrangement, the axis of the link 4is always substantially coplanar with the axis of the crank arm 20 sothat the opposing forces acting through the mechanism transmit motionwithout developing a torque about the axis of the crank arm. This avoidsthe problem which has previously caused degraded altitude readings whenthe altimeter reverts to the pressure actuated mode after excessivecorrection has been applied.

Iclaim:

I. In an altimeter having a pressure sensitive capsule movable in alinear function, a rocking shaft movable in a rotating function inpredetermined relation with respect to the capsule, mechanism forimparting corrective force and movement to the rocking shaft inopposition to the capsule, and bimetallic temperature compensating meanshaving first and second opposed end regions, the first of said endregions being connected with said capsule, a support connecting saidrocking shaft with said compensator means for determining a motiontransfer function between said rocking shaft and said capsule when thealtimeter reverts to its pressure actuated mode, said support includinga base, an upstanding arm extending upwardly from the base, and a crankarm having an axis and extending transversely from the vertical arm nearthe top portion thereof, the end region of said crank arm remote fromsaid vertical arm being adapted for adjustable connection with saidrocking shaft to adjustably locate said base alongside the rockingshaft, said base having a pair of adjustable jaw portions for adjustablygripping the second of said end regions of said compensator means tolocate said compensator means alongside said vertical arm andsubstantially parallel to the axis of said rocking shaft so that thefirst of said end regions of said compensator means and the axis of saidcrank arm determine a plane substantially normal to the axis of saidrocking shaft.

2. In an altimeter having a pressure sensitive capsule movable in alinear function, a rocking shaft movable in a rotating function inpredetermined relation with respect to the capsule, and mechanism forimparting corrective force and movement TO THE ROCKING SHAFT INOPPOSITION TO THE CAP- SULE, a calibration arm assembly connected inboth force and travel transmitting relation between the capsule androcking shaft for determining a motion transfer function therebetweenwhen the altimeter reverts to its pressure actuated mode, said assemblyincluding a support having a trans verse crank arm having an axis andextending through the rocking shaft to locate the support alongside therocking shaft, temperature compensatlng means mounted to the support,and a link having an axis and connected between the capsule and thecompensating means, the support mounting the compensating means so thatthe axis of the link is in a common plane with the axis of the crank armwhich plane is generally transverse to the axis of the rocking shaft toenable transmission of opposing forces between the capsule and rockingshaft free of torque about the axis of the crank arm, whereby theaccuracy when the altimeter reverts to its pressure actuated mode is notdegraded by the opposing forces previously acting through thecalibration arm assembly.

3. In an altimeter in accordance with claim 2 wherein said plane isnormal to the axis of the rocking shaft.

4. In an altimeter calibration arm assembly for connecting in both forceand travel transmitting relation a pressure sensitive capsule of thealtimeter with a rocking shaft thereof, the assembly including anelongated bimetallic temperature compensator element having a pair ofopposite end regions, one of said end regions being connected through alinkage with the capsule, a support for connecting said compensatorelement with said rocking shaft, the improvement wherein said supportcomprises a base, an upstanding arm extending upwardly from the base,and a crank arm having an axis and extending transverscly from theupstanding arm near the top portion thereof, the end region of saidcrank arm remote from said vertical arm being adapted for adjustableconnection with said rocking shaft to adjustably locate said basealongside the rocking shaft, said base having clamping means foradjustably gripping the other of said end regions of said compensatorelement to locate said compensator element alongside said vertical armand substantially parallel to the axis of said rocking shaft so thatsaid one of said end regions of said compensator element and the axis ofsaid crank arm determine a plane substantially normal to the axis ofsaid rocking shaft.

1. In an altimeter having a pressure sensitive capsule movable in alinear function, a rocking shaft movable in a rotating function inpredetermined relation with respect to the capsule, mechanism forimparting corrective force and movement to the rocking shaft inopposition to the capsule, and bimetallic temperature compensating meanshaving first and second opposed end regions, the first of said endregions being connected with said capsule, a support connecting saidrocking shaft with said compensator means for determining a motiontransfer function between said rocking shaft and said capsule when thealtimeter reverts to its pressure actuated mode, said support includinga base, an upstanding arm extending upwardly from the base, and a crankarm having an axis and extending transversely from the vertical arm nearthe top portion thereof, the end region of said crank arm remote fromsaid vertical arm being adapted for adjustable connection with saidrocking shaft to adjustably locate said base alongside the rockingshaft, said base having a pair of adjustable jaw portions for adjustablygripping the second of said end regions of said compensator means tolocate said compensator means alongside said vertical arm andsubstantially parallel to the axis of said rocking shaft so that thefirst of said end regions of said compensator means and the axis of saidcrank arm determine a plane substantially normal to the axis of saidrocking shaft.
 2. In an altimeter having a pressure sensitive capsulemovable in a linear function, a rocking shaft movable in a rotatingfunction in predetermined relation with respect to the capsule, andmechanism for imparting corrective force and movement TO THE ROCKINGSHAFT IN OPPOSITION TO THE CAPSULE, a calibration arm assembly connectedin both force and travel transmitting relation between the capsule androcking shaft for determining a motion transfer function therebetweenwhen the altimeter reverts to its pressure actuated mode, said assemblyincluding a support having a transverse crank arm having an axis andextending through the rocking shaft to locate the support alongside therocking shaft, temperature compensatIng means mounted to the support,and a link having an axis and connected between the capsule and thecompensating means, the support mounting the compensating means so thatthe axis of the link is in a common plane with the axis of the crank armwhich plane is generally transverse to the axis of the rocking shaft toenable transmission of opposing forces between the capsule and rockingshaft free of torque about the axis of the crank arm, whereby theaccuracy when the altimeter reverts to its pressure actuated mode is notdegraded by the opposing forces previously acting through thecalibration arm assembly.
 3. In an altimeter in accordance with claim 2wherein said plane is normal to the axis of the rocking shaft.
 4. In analtimeter calibration arm assembly for connecting in both force andtravel transmitting relation a pressure sensitive capsule of thealtimeter with a rocking shaft thereof, the assembly including anelongated bimetallic temperature compensator element having a pair ofopposite end regions, one of said end regions being connected through alinkage with the capsule, a support for connecting said compensatorelemenT with said rocking shaft, the improvement wherein said supportcomprises a base, an upstanding arm extending upwardly from the base,and a crank arm having an axis and extending transversely from theupstanding arm near the top portion thereof, the end region of saidcrank arm remote from said vertical arm being adapted for adjustableconnection with said rocking shaft to adjustably locate said basealongside the rocking shaft, said base having clamping means foradjustably gripping the other of said end regions of said compensatorelement to locate said compensator element alongside said vertical armand substantially parallel to the axis of said rocking shaft so thatsaid one of said end regions of said compensator element and the axis ofsaid crank arm determine a plane substantially normal to the axis ofsaid rocking shaft.